1. Field of the Invention
The present invention relates to a thermal expansion valve for a refrigerating cycle in an automotive air conditioning system, for example. More particularly, the present invention relates to a thermal expansion valve having a temperature sensing portion for preventing a hunting from being caused in the thermal expansion valve.
2. Description of Related Art
Generally, an expansion valve of a refrigerating cycle senses a temperature of refrigerant at an outlet of an evaporator and adjusts a flow amount of refrigerant of the refrigerant cycle by changing a valve opening degree of a valve body so that a superheating degree of refrigerant at the outlet of the evaporator is maintained at a predetermined value according to a variation of a heat load of the evaporator.
In an automotive air conditioning system, by a variation of a rotational speed of an engine used as a driving source of a compressor and a rapid variation of the heat load of the evaporator, the temperature sensing portion for sensing a temperature of refrigerant at the outlet of the evaporator is operated to frequently changes the valve opening degree. Therefore, the hunting is caused in the expansion valve.
When the hunting caused in the expansion valve becomes severe, the temperature of air to be blown into the passenger compartment greatly changes so that an unpleasant feeling is given to a passenger in a passenger compartment.
To suppress the hunting from being caused in the expansion valve, in an expansion valve described in JOURNAL OF NIPPONDENSO TECHNICAL DISCLOSURE NO. 68-153 published on Nov. 15, 1989, outer surfaces of a part of temperature sensing rod, placed at a side of a diaphragm and a diaphragm stopper, are formed of a resinous material having a small heat conductivity.
However, in the conventional expansion valve, because the temperature sensing rod is directly exposed to a refrigerant passage at an evaporator outlet side, the temperature of refrigerant at the evaporator outlet side is excessively sensitively sensed by the exposed portion of the temperature sensing rod. Therefore, the hunting caused in the expansion value cannot be suppressed sufficiently.